Why would a developer not want to deliver traffic to everyone with HTML5 video? There an inherently higher cost (bandwidth) or something that I'm unaware of? Se

Why would a developer not want to deliver traffic to everyone with HTML5 video? There an inherently higher cost (bandwidth) or something that I'm unaware of? Seems if I have the video in a format that will work for HTML5, that I'd want to deliver it as that if the user's browser can deal with it.